The translation level control of protein synthesis in early development is being investigated. Eggs contain a store of inactive messanger RNA (mRNA) which begins to be translated at a high level with the start of development. The messenger ribonucleo-protein particles (mRNP) which contain this mRNA are being isolated and characterized. These particles are being compared with mRNP particles isolated from embryo polysomes. Methods for isolation of mRNPs and specific assays for RNA sequences contained in mRNPs are being developed as are methods for in vitro translation of these particles.